Asphalt-based coating compositions are used in a broad range of applications wherein it is desired to construct, coat, patch, join, fill and repair a diverse range of articles and things. Exemplary applications for asphalt-based coating compositions include use in roof construction and repair, pavement construction and repair and use as a durable, protective coating for application to buildings, surfaces and mechanical and electrical apparatus.
Asphalt-based coating compositions are supplied to both the industrial and consumer markets. Coating compositions for use in these separate markets are typically formulated using different base constituents. Consumer-market coating compositions typically comprise an admixture of asphalt cutback, clay and surfactant as base constituents. The asphalt cutback constituent is provided as a binder. The clay constituent thickens the composition and provides gelling properties. The surfactant constituent is provided to wet and disperse the clay and asphalt cutback constituents by reducing interfacial tension.
Industrial-market coating compositions commonly utilize a base formulation comprising either an admixture of asphalt cutback, clay and surfactant or a formulation comprising asphalt cutback and asbestos. Such asbestos-containing compositions can include as much as fifty weight percent of asbestos. The asbestos imparts bulk to the coating composition and provides excellent adhesion within the asphalt constituents.
There are, however, disadvantages associated with the use of asbestos. Asbestos must be handled carefully due to potential toxicity problems associated with the handling and disposal of this material. Environmental and compliance costs associated with asbestos can be prohibitively high. Asbestos is banned in some communities and is not used in the consumer coating marketplace thereby requiring a formulator to make different coating compositions for different geographic regions and markets resulting in increased costs.
The coatings industry is extremely cost competitive. There is an ongoing effort to develop asphalt-based coating compositions which provide improved performance yet cost less. As those of skill in the art are aware, small price differences per unit volume of coating can have a significant effect on product sales and can mean the difference between success or failure in the marketplace.
One way to control cost is to formulate asphalt-based coating compositions which are free of asbestos. However, if asbestos is not used then the surfactant must be capable of dispersing and wetting the coating constituents thereby imparting the desired viscosity to the compositions. The surfactant cost is typically high relative to the cost of the other coating constituents.
Another way to control cost is to reduce the amount of surfactant required. The amount of surfactant utilized is commonly expressed in terms of the ratio of clay to surfactant (the “C/S ratio”). The C/S ratio is the ratio of the weight percentage of clay to the weight percentage of surfactant in the overall composition. The C/S ratio is a useful measure of surfactant content because asphalt cutback is the predominant constituent of the coating formulations and the amount of asphalt cutback typically does not vary greatly with respect to the amount of clay and surfactant utilized. The higher the C/S ratio the lower the amount of surfactant composition used and the lower the cost of the resultant coating.
Asbestos-free asphalt-based roof coating compositions typically have a C/S ratio in the range of about 7:1 to about 10:1. A surfactant capable of producing the same or similar results to known coating compositions at a higher C/S ratio would potentially present an opportunity to control costs.
Asphalt-based coating compositions should also be easy to manufacture and formulate in order to further control cost. By way of example, older asbestos-free roof coating compositions were based on quaternary ammonium chloride salt surfactants (particularly dialkyl quaternary ammonium chlorides) and these surfactants were difficult to use thereby imposing costs on the formulator. Quaternary ammonium chloride salts were difficult to use because they are typically in a solid or paste-like form at room temperature thereby making it difficult to admix the surfactant with the other coating constituents and to obtain a homogenous mixture. In order to utilize these types of surfactants, they must first be liquified, either by admixture with solvents or by heating the surfactants. The use of solvents is disadvantageous because of cost and because the end product comprises less than 100% active surfactant. Heating the surfactant adds a further processing step and presents the potential for the decomposition and deactivation of the surfactant. And, heating the surfactant raises potential fire hazard concerns, particularly if flammable solvents are present in the surfactant.
Quaternary ammonium chloride salts were also found to be corrosive making them difficult to package and store. Such corrosivity limited the use of the asphalt-based coating compositions with corrosion-prone metals, such as automobile underbodies.
Costs can be further controlled and coating quality improved by providing a surfactant which is robust and capable of imparting appropriate viscosity to asphalt-based compositions including a wide range of asphalts, clays and other constituents. Asphalts used to make asphalt cutbacks, lack uniformity and vary greatly in constituents. As is well known in the coating manufacturing industry, asphalts may be oxidized or unoxidized, depending upon the grade desired and the practice of the asphalt manufacturer. Oxidization of the asphalt can greatly affect its characteristics. Other asphalt cutback constituents can vary significantly. Seemingly similar coating material constituents can vary widely in material properties depending on the geographic region from which such materials are refined, mined or otherwise obtained. Inability of the surfactant to wet and disperse a wide range of constituents will result in loss of viscosity and cause premature failure of the composition. Conversely, a surfactant having efficacy with a broad range of coating constituents would provide an improved product while reducing costs to the formulator.
There has been considerable interest in asphalt-based coating compositions and surfactants for wetting and dispersing coating composition constituents in the patent literature. Examples include U.S. Pat. No. 4,759,799 (Vicenzi), U.S. Pat. No. 5,618,340 (Krogh et al.), U.S. Pat. No. 5,622,554 (Krogh et al.), U.S. Pat. No. 5,730,791 (Krogh et al.), U.S. Pat. No. 6,169,064 (Krogh et al.), U.S. Pat. No. 5,693,133 (Largent et al.), U.S. Pat. No. 5,529,621 (Hudson et al.) and U.S. Pat. No. 5,662,733 (Hudson et al.).
And, a number of asphalt-based coating compositions are commercially available. Representative compositions include No. 100 Elastomulsion® and No. 107 Asphalt Emulsion available from the Henry Company of Huntington Park, Calif., Redicote® brand emulsions available from Akzo Nobel Chemicals, Inc. of Willowbrook, Ill. and No. 71AF Fibered Asphalt Coating, No. 229AR Elastomeric, No. 100AF Non-Fibered Emulsion Coating, No. 107 Velvet Roof Coating and No. 112AF Foundation & Roof Coatings available from Karnak Corporation of Clark, N.J.
The industry standard surfactant used with many commercially-available asphalt-based coating compositions is PA-14 Acetate™ surfactant available from Tomah Products, Inc. of Milton, Wis. PA-14 Acetate is an isodecyloxypropyl amine acetate salt surfactant.
There is nonetheless, an ongoing need for cost-effective asphalt-based coating compositions with improved viscosity and gel stability, which are easy to manufacture and apply, which are free of any requirement for asbestos, which are robust and capable of being used with a wide variety of coating constituents and which avoid the disadvantages of prior art coating compositions. And, there is an ongoing need for improved surfactants capable of use in such compositions.